1. Field of the Invention
The present invention relates to a novel photosensitive composition suitably used to manufacture semiconductor devices or multilayer circuit boards in the field of electric and electronics. Particularly, this invention relates to a photosensitive composition applicable to a lithography process with a short wavelength light source in order to obtain polyimide patterns after annealing. Such a composition is becoming popular in the production process of semiconductors.
2. Prior Art
Polyimides have been recognized as a material used in the field of electronics for their high thermal and chemical stabilities, low dielectric constant and excellent ability in planarization. These polyimides have been widely used as materials for surface protective layers, interlayer dielectrics of semiconductors and insulating layers in multichip modules.
In order to obtain a desired pattern from ordinary polyimide coatings, an indirect lithographic method wherein, for example, a polyimide layer with patterned photoresist as an etching mask is etched is employed. In this method, however, the process is complicated. Moreover, the method has drawbacks such as the use of harmful agents like hydrazine is required in the etching process and the resolution of the polyimide pattern is reduced because of the indirect lithographic method.
Accordingly, investigations into methods for direct pattern formation of polyimides with photoreactive compounds having polyimides or polyimide precursors have been conducted. In such methods, the polyamic acid derivatives having double bonds linked through ester bonds, amide bonds, acid ammonium salt and the like are used. The polyamic acid derivatives can be used in the direct photolithography process with photo initiators. The photosensitive components are removed by heating to obtain thermally stable polyimides (T. Yamaoka and T. Omote, xe2x80x9cPolyfilexe2x80x9d, vol.27, no.2, pp.14-18 (1990)). This technology is generally referred to as a photosensitive polyimide technology.
A demand for accumulation of semiconductors such as IC, LSI, VLSI has been gradually increasing. According to this demand, processing technologies for fine materials has been expected. In one of the technologies, the pattern formation of photoresists is conducted by using short wavelength light such as i-line light of Hg lamp (365 nm wavelength) instead of ordinary G-line light (436 nm wavelength), for which a high resolution can be expected. It has been anticipated that all exposure apparatus will employ i-line light at semiconductor munufacturing factories in the near future.
On the other hand, in the case of conventional polyimide precursor technology, the compositions to be used in this technology have relatively high absorbance to i-line light. Further, the polyimide precursor compositions are applied to be rather thick, that is, 12 xcexcm or more, in view of the shrinkage caused by removing the photosensitive components during curing, because the polyimide coating requires 6 xcexcm thick or more from the standpoint of the physical properties. Therefore, conventional polyimide precursor compositions do not allow i-line light to reach the bottom of its coating. As a result, the bottom of the coating is not sufficiently hardened by exposure and the pattern is washed away in development. Consequently, i-line light is not suitable for the exposure light source for obtaining a polyimide coating having more than a certain thickness. (C. Schuoket, et al., xe2x80x9cIEEE/SEMI Advanced Semiconductor Manufacturing Conferencexe2x80x9d, pp.72-74 (1990))
When i-line light is used, a pattern formation of thin coatings must be conducted several times to obtain sufficiently thick polyimide coating, so that the accuracy of the resultant patterns cannot be improved and the production process becomes complicated. Therefore, i-line light exposure is not practical.
It has been known that a film of a fluorine-containing polyimide precursor has high i-line light trasmittancy (T. Omote, T. Yamaoka and K. Kosei, xe2x80x9cJournal of Applied Polymer Siencexe2x80x9d, vol.38, pp.389-402 (1989)). Polyimides, which are obtained by heat-curing the precursors and contain fluorine in their main frame work, have drawbacks in practical use. That is, they have a low adhesive strength to other materials used with polyimides, such as base inorganic materials, epoxy resins in coating layers and metals for distributing wires when they are used for semiconductor devices and multilayer circuit boards. A photosensitive polyimide precursor composition, which can form patterns by means of i-line light and is applicable to practical uses, has not yet been obtained.
The present invention provides a photosensitive polyimide composition. From the composition, a polyimide film having more than a certain thickness can be obtained by taking the process of pattern formation by i-line exposure and a heat-cure. The composition is applicable to practical uses.
A desirable pattern is formed by exposing the photosensitive polyimide precursor composition to i-line light, which composition comprises polyimide precursors having a chemical structure selected from several specific chemical structures and/or specific amide bond density and is adjusted so that the film obtained by applying and drying the composition may exhibit specific absorbance. The polyimide film obtained by heat-curing the above pattern exhibits excellent physical properties and water resistance, and has high adhesive strength to epoxy resins, inorganic materials and metals.
The present invention provides photosensitive compositions comprising:
(A) an aromatic polyimide precursor (hereinafter referred to as a polyimide precursor) having amide bond density of 1.5 mol/kg or more and a repeating unit represented by the general formula (I): 
xe2x80x83wherein X represents a tetravalent aromatic radical not including a fluorine atom or a tetravalent organic radical having a chemical structure in which 2 to 4 aromatic radicals are linked through at least one type of bond selected from the group consisting of a single bond, an ether bond, a thioether bond, a carbonyl bond, a methylene bond, a sulfoxide bond and a sulfone bond, and which does not include a fluorine atom; xe2x80x94COR and xe2x80x94CORxe2x80x2 groups take the ortho positions against xe2x80x94CONH group; R and Rxe2x80x2 independently represent xe2x80x94OR1, xe2x80x94NHR2, xe2x80x94Oxe2x88x92N+R3R4R5R6 or xe2x80x94OH groups, wherein R1 to R3 represent organic radicals having olefinically unsaturated bonds at least in part of the repeating units and may coexisit in the repeating units; and R4 to R6 independently represent a hydrogen atom or a hydrocarbon radical having 1 to 6 carbon atoms, and R or Rxe2x80x2, contained at least in part of repeating units, represents a residual group except for xe2x80x94OH; and Y represents a divalent aromatic radical not including a fluorine atom or a divalent organic radical having a chemical structure in which 2 to 6 aromatic radicals are linked through at least one type of bond-selected from the group consisting of a single bond, an ether bond, a thioether bond, a carbonyl bond, a methylene bond, a 2,2-propylene bond, a sulfoxide bond and a sulfone bond, and which does not include a fluorine atom,
(B) a photopolymerization initiator, and
(C) a solvent.
Moreover, the polyimide precursor of the photosensitive composition satisfies at least one of the following conditions:
(i) amide bond density is 2.42 mol/kg or less,
(ii) X is a tetravalent radical wherein the aromatic radicals connected with xe2x80x94CONH groups has a chemical structure in which the aromatic radical is substituted with aprotic electron donating group, and
(iii) Y is a divalent radical:
(iii-1) represented by the general formula (II): 
xe2x80x83wherein R7 represents an aliphatic hydrocarbon radical having 1 to 4 carbon atoms and n represents an integer of 0 to 3,
(iii-2) represented by the general formula (III): 
xe2x80x83wherein A represents xe2x80x94CH2xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, a m-dioxyphenylene radical, a p-dioxyphenylene radical or a group represented by the general formula (III-1): 
xe2x80x83wherein B represents xe2x80x94CH2xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, a m-dioxyphenylene radical or a p-dioxyphenylene radical; and k represents 0 or 1; and m represents 0 or 1,
(iii-3) represented by the general formula (IV): 
xe2x80x83wherein C represents xe2x80x94SO2xe2x80x94, xe2x80x94SOxe2x80x94 or xe2x80x94COxe2x80x94, p represents 0, 1 or 2 and Z represents xe2x80x94Oxe2x80x94, xe2x80x94CH2xe2x80x94 or 
xe2x80x83or
(iii-4) wherein an aromatic radical connected with xe2x80x94NHxe2x80x94 or an aromatic radical adjacent to such an aromatic radical through an ether bond has a chemical structure in which the aromatic radical is substituted with aprotic electron attracting group.
A film, which is obtained by applying and drying the photosensitive composition, has absorbance of 1.5 or less per 10 xcexcm thick at 365 nm wavelength light.
In the composition of the present invention, the polyimide precursor used as component (A) is represented by the general formula (I).
As for each aromatic radical contained in X and Y in the general formula (I), groups having a benzene ring, a naphthalene ring or an anthracene ring are preferred because the heat resistance of a polyimide film obtained by heat-curing the photosensitive composition having such radicals is high. As for the type of bond between the aromatic radicals, one or more selected from the group consisting of a single bond, an ether bond, a carbonyl bond and a sulfone bond are preferred because of the the same reason as mentioned above.
When the xe2x80x94COR or xe2x80x94CORxe2x80x2 group in the general formula (I) is an ester group represented by the general formula (V-1):
xe2x80x94COOR1xe2x80x83xe2x80x83(V-1)
wherein R1 is as defined above,
it is necessary that the ester group includes a group having an olefinically unsaturated bond such as a 2-acryloyloxyethyl-oxycarbonyl radical, a 2-methacloyloxyethloxycarbonyl radical, a 2-(1-acryloyloxy)propyloxycarbonyl radical, 2-(1-methacloyloxy)-propyloxycarbonyl radical, a 2-methacryl-aminoethyloxycarbonyl radical, a 3-methacloyloxy-2-hydroxy-propyloxycarbonyl radical and an acrylaminomethyloxycarbonyl radical. Additionally, the ester group may include a group not having an olefinically unsaturated bond such as an ethoxycarbonyl radical, a methoxycarbonyl radical, a 2-methoxy-ethoxycarbonyl radical or a 2-ethoxyethoxy-carbonyl radical.
When the xe2x80x94COR or xe2x80x94CORxe2x80x2 group in the general formula (I) is an amide group represented by the general formula (V-2):
xe2x80x94CONHR2xe2x80x83xe2x80x83(V-2)
wherein R2 is as defined above,
it is necessary that the amide group includes a group having an olefinically unsaturated bond such as a N-(2-acryloyloxyethyl)aminocarbonyl radical and N-(2-methacryloxyethyl)aminocarbonyl radical. Additionally, the amide group may include a group not having an olefinically unsaturated bond such as a methylaminocarbonyl radical, a ethylaminocarbonyl radical or a N-(2-ethoxyethyl)aminocarbonyl radical.
When the xe2x80x94COR or xe2x80x94CORxe2x80x2 group in the general formula (I) is an ammonium salt of carboxylic acid represented by the general formula (V-3):
xe2x80x94COOxe2x80x94.N+R3R4R5R6xe2x80x83xe2x80x83(V-3)
wherein R3, R4, R5 and R6 are as defined above,
it is necessary that the ammonium salt of carboxylic acid includes a group having an olefinically unsaturated bond such as a carboxylic acid 2-methacloyloxyethyl-trimethylammonium salt or a carboxylic acid 2-acryloyloxyethyl-dimethylammonium salt. Additionally, the ammonium salt of carboxylic acid may include a group not having an olefinically unsaturated bond wherein all the R3 to R6 are hydrogen atoms or hydrocarbon radicals.
When the xe2x80x94COR or xe2x80x94CORxe2x80x2 group in the general formula (I) is a carboxylic acid group, it is necessary that the groups mentioned in the general fomulas (V-1), (V-2) or (V-3) also exist in the repeating units of the polyimide precursor.
A polyimide precursor, which has a group selected from the groups represented by the general formulas (V-1), (V-2) and a carboxylic acid, and in which at least part of the repeating units has a residual group except a carboxylic acid, is preferably used because a coating thickness of the obtained photosensitive composition is almost unchanged during development and the polyimide pattern has good reproducibility from the photomask and has high resolution. A polyimide precursor, which has only the ester group represented by the general formula (V-1), is more preferably used because the obtained photosensitive composition has good storage stability and wide process margin for patterning, that is, the pattern is almost unchanged depending on a fluctuation of process conditions such as a process period in patterning, temperature.
In the composition of the present invention, the polyimide precursor used as component (A) should have amide bond density of 1.5 mol/kg or more. The amide bond density means a value obtained by dividing 2000 by a molecular weight of the repeating unit of the polyimide precursor or a value obtained by dividing 2000 by an average molecular weight, which is calculated from a molecular weight of each repeating unit and a molar ratio of each repeating unit if the polyimide precursor has several kinds of the repeating unit. The amide bond density is a parameter representing a mole value of an amide group present in 1 kg of the polyimide precursor. When the amide bond density is lower than 1.5 mol/kg, heat resistance is considerably degraded.
The polyimide precursor used represented by the general formula (I) is well-known as a precursor of a heat resistant macromolecule and is produced by known methods described by, for example, R. Rubner et al. (xe2x80x9cPhotographic Science Engineeringxe2x80x9d, vol.23, p.303 (1979)), M. T. Pottiger et al. (xe2x80x9cThe 38th Electronic Components Conferencexe2x80x9d, p.315 (1988)), L. Minnema et al. (xe2x80x9cPolymer Engineering and Sciencexe2x80x9d. vol.28, no.12, p.815 (1988)) and Davis et al. (xe2x80x9cChemical and Engineering News; Sep. 26, 1983xe2x80x9d, p.23). Additionally, the polyimide precursor can be also produced by the methods described in U.S. Pat. Nos. 4,645,823 and 4,243,743, European Patent Unexamined Publication No. 421,195 and Japanese Patent Application Laid-Open No. 4226/1991.
According to these methods, the polyimide precursor is produced by using an aromatic tetracarboxylic dianhydride (hereinafter referred to as ATC dianhydride) represented by the general formula (VI), an aromatic diamino compound represented by the general formula (VII) as a part of raw materials. 
wherein X is as defined above.
H2Nxe2x80x94Yxe2x80x94NH2xe2x80x83xe2x80x83(VII)
wherein Y is as defined above.
When a compound having a group containing a fluorine atom such as a fluorine group and a trifluoromethyl group is used as a raw material for the polyimide precursor of the present invention, a fluorine-containing polyimide obtained by heat-curing the photosensitive composition is not applicable to practical uses because of its low adhesive strength to other material.
It is necessary to use a polyimide precursor satisfying at least one or more specific conditions in order to obtain the photosensitive composition of the present invention. Specific conditions mean the conditions (i) to (iii-4) mentioned above. As long as the photosensitive composition of the present invention satisfies the other conditions described in the above, conditions (i) to (iii-4) can be used without any restriction.
The amide bond density must be at least 1.5 mol/kg as mentioned above. When the amide bond density is 2.42 mol/kg or less and the condition of polyimide precursor described in (A) is satisfied, the composition of the present invention can be obtained regardless of the structure of the polyimide precursor and i-line absorbance of the obtained polymer coating becomes lower and water resistance of the heat-cured film becomes higher with a decrease in the amide bond density. The polyimide precursor having amide bond density of from 2.0 to 2.42 mol/kg is preferred because the obtained polyimide film has higher mechanical strength and heat resistance.
For the preparation of the polyimide precursor satisfying condition (ii), an ATC dianhydride is used, wherein the aromatic radical having a carboxylic anhydride group has a chemical structure in which the aromatic radical is substituted with an aprotic electron donating group (hereinafter referred to as ATC dianhydride under condition (ii)xe2x80x2). Herein, the aprotic group may not be a group having active hydrogen such as an alcohol, an amine and a carboxylic acid. The electron donating group indicates a substituting group, whose value of "sgr"p or "sgr"m is minus in Hammett""s rule. The rule and value are widely known, for example, Section 365 of xe2x80x9cKagaku Binran Kisohen IIxe2x80x9d edited by Nippon Kagaku Kai and published by Maruzen Company, Limited in 1984. Representative examples of the aprotic electron donating groups include a dialkylamino group, an alkoxy group, an aryloxy group, a trialkylsilyl group, a benzyl group and an alkyl group. Representative examples of the ATC dianhydrides under condition (ii)xe2x80x2 include 3,3xe2x80x2,4,4xe2x80x2-diphenylether tetracarboxylic dianhydride, 1,4-dimetoxy-2,3,5,6-benzene tetracarboxylic dianhydride, 1,4-ditrimethylsilyl-2,3,5,6-benzene tetracarboxylic dianhydride, 1,4-bis-(3,4-dicarboxylphenoxy)benzene dianhydride, 1,3-bis(3,4-dicarboxylphenoxy)benzene dianhydride, 3,3xe2x80x2,4,4xe2x80x2-diphenylmethane tetracarboxylic dianhydride, bis(3,4-dicarboxylphenoxy)dimethylsilane dianhydride, bis(3,4-dicarboxylphenoxy)methylamine dianhydride, 4,4xe2x80x2-bis(3,4-dicarboxylphenoxy)biphenyl dianhydride and 4,4xe2x80x2-bis(3,4-dicarboxylphonoxy)diphenylsulfone dianhydride.
In the present invention, as long as the absorbance of a coating obtained from the photosensitive composition is 1.5 or less per 10 xcexcm thick at 365 nm wavelength, the ATC dianhydride represented by the general formula (VI) other than the one under condition (ii)xe2x80x2 can be used: (1) by mixing with the ATC dianhydride under condition (ii)xe2x80x2; (2) by combining with the specific aromatic diamino compound mentioned below; or (3) if an aromatic polyimide precursor having specific amide bond density is obtained. Representative examples of these compounds include pyromellitic dianhydride, 2,3,5,6-naphthalene tetracarboxylic dianhydride, 3,3xe2x80x2,4,4xe2x80x2-benzophenone tetracarboxylic dianhydride, 3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride, 2,3,5,6-pyridine tetracarboxylic dianhydride, 2,3,6,7-quinoline tetracarboxylic dianhydride, 3,3xe2x80x2,4,4xe2x80x2-diphenylsulfone tetracarboxylic dianhydride, 3,3xe2x80x2,4,4xe2x80x2-diphenylsulfide tetracarboxylic dianhydride and 3,3xe2x80x2,4,4xe2x80x2-diphenylsulfoxide tetracarboxylic dianhydride. In addition, they include 1,2,8,9-anthracene tetracarboxylic dianhydride, 1,4-bis(3,4-dicarboxylphenylsulfonyl)benzene dianhydride, 1,4-bis(3,4-dicarboxylphenylthio)benzene dianhydride, 3,3xe2x80x3,4,4xe2x80x3-terphenyl tetracarboxylic dianhydride, 4-phenylbenzophenone-3,3xe2x80x3,4,4xe2x80x3-tetracarboxylic dianhydride, 1,4-bis-(3,4-dicarboxylbenzoyl)-benzene dianhydride, 3,3xe2x80x2xe2x80x3,4,4xe2x80x2xe2x80x3-quaterphenyl tetracarboxylic dianhydride, 4,4xe2x80x2-bis(3,4-dicarboxylphenoxy)-benzophenone dianhydride and 4,4xe2x80x2-bis(3,4-dicarboxylphenoxy)-diphenylsufoxide dianhydride.
For the preparation of the aromatic polyimide precursor satisfying condition (iii-1), an aromatic diamino compound wherein Y is a divalent group represented by the general formula (II) (hereinafter referred to as an aromatic diamino compound under condition (iii-1)xe2x80x2) is used. Representative examples of the aromatic diamino compounds include methaphenylenediamine, 3,5-diaminotoluene, 2,4-diaminotoluene and 2,4-diaminomesitylene.
For the preparation of the aromatic polyimide precursor satisfying condition (iii-2), an aromatic diamino compound wherein Y is a divalent group represented by the general formula (III) (hereinafter referred to as an aromatic diamino compound under condition (iii-2)xe2x80x2) is used. Representative examples of the aromatic diamino compounds include 4,4xe2x80x2-bis(3-aminophenoxy)bipenyl, 1,3-bis(3-aminophenoxy)benzene, 3,3xe2x80x2-diaminobiphenyl, 3,3xe2x80x2-diaminodiphenylether, 3,3xe2x80x2-diaminodiphenylsulfone, 3,3xe2x80x2-diamino-benzophenone, 3,3xe2x80x2-diaminodiphenylmethane, 3,3xe2x80x2-diamino-diphenylsulfide, 4,4xe2x80x2-bis(3-aminophenoxy)diphenylsulfone, 4,4xe2x80x2-bis(3-aminophenoxy)diphenylmethane, 4,4xe2x80x2-bis(3-aminophenoxy)diphenylether and 4,4xe2x80x2-bis(3-aminophenoxy)-diphenylsulfide.
For the preparation of the aromatic polyimide precursor satisfying condition (iii-3), an aromatic diamino compound wherein Y is a divalent group represented by the general formula (IV) (hereinafter referred to as an aromatic diamino compound under condition (iii-3)xe2x80x2) is used. Representative examples of the aromatic diamino compounds include 4,4xe2x80x2-diaminodiphenylsulfone, 4,4xe2x80x2-diamino-benzohenone, 4,4xe2x80x2-diaminodiphenylsulfoxide, 4,4xe2x80x2-bis(4-aminophenoxy)diphenylsulfone, 4,4xe2x80x2-bis(4-aminophenoxy)diphenylsulfoxide and 4,4xe2x80x2-bis(4-aminophenoxy)benzophenone.
For the preparation of the aromatic polyimide precursor satisfying condition (iii-4), an aromatic diamino compound wherein an aromatic radical having an amino group or an aromatic radical adjacent to such an aromatic radical linked through an ether bond has a chemical structure in which the aromatic radical is substituted with an aprotic electron attracting group (hereinafter referred to as an aromatic diamino compound under condition (iii-4)xe2x80x2) is used. The electron attracting group used herein indicates a substituting group having 0.2 or more of xcex4p or xcex4m value mentioned above. Aprotic electron attracting groups include an acyloxy group, an acylamino group, a halogen group, an alkylaminocarbonyl group, an alkoxycarbonyl group, an alkylcarbonyl group, a nitrile group, an alkylsulfone group, a nitro group and an alkoxysulfone group. Representative examples of the aromatic amino compounds under condition (iii-4)xe2x80x2 include 4,4xe2x80x2-diamino-benzophenone, 4,4xe2x80x2-diaminodiphenylsulfone, 3,3xe2x80x2-diamino-diphenylsulfone, 4,4xe2x80x2-diaminodiphenylsulfoxide, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4xe2x80x2-bis[4-(4-aminophenoxy)phenylsulfonyl]diphenylether, bis[4-(3-aminophenoxy)phenyl]sulfone, 4,4xe2x80x2-bis(4-aminophenoxy)benzophenone, 1,4-bis(4aminophenylsulfonyl)benzene, 1,4-bis[4-(4-aminophenoxy)phenylsulfonyl]benzene, 4,4xe2x80x2-bis(4-aminophenylsulfonyl)diphenylether, 3,5-diaminoethylbenzoate, 2,4-diaminobenzamide, 3,5-diaminobenzophenone, 4-dimethyl-amino-3xe2x80x2,5xe2x80x2-diamino-benzophenone, 3,5-diamino(2-methacryloxyethyl)benzoate, 3,5-diaminoacetanilide, 4-chloro-m-phenylenediamine, 3,5-diaminobenzonitrile and 5-nitro-m-phenylenediamine.
In the present invention, as long as the absorbance of a coating obtained from the photosensitive composition is 1.5 or less per 10 xcexcm thick at 365 nm wavelength, the aromatic diamino compound represented by the general formula (VII) other than the specific aromatic diamino compound mentioned above can be used: (1) by mixing with the specific aromatic diamino compound mentioned above; (2) by combining with the ATC dianhydride under condition (ii)xe2x80x2; or (3) if an aromatic polyimide precursor having specific amide bond density is obtained. Representative examples of the aromatic diamino compounds, include 4,4xe2x80x2-diaminodiphenylether, 4,4xe2x80x2-diaminodiphenylsulfide, 3,4xe2x80x2-diaminodiphenylether, 1,4-phenylenediamine, 2,7-naphthalenediamine, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminobiphenyl, 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diaminobiphenyl, 3,3xe2x80x2-dichloro-4,4xe2x80x2-diaminobiphenyl, 1,4-bis(4-aminophenoxy)-benzene, 1,3-bis(4-aminophenoxy)benzene, 5,8-diaminoquinoline, 4,4xe2x80x2-bis(4-aminophenoxy)biphenyl, 4,4xe2x80x2-diaminodiphenylmethane, bis[4-(4-aminophenoxy)phenyl]ether, 1,4-bis(4-aminophenyl)-benzene, 9,10-bis(4-aminophenyl)anthracene, 4,4xe2x80x2-bis(4-aminophenoxy)diphenylmethane, 4,4xe2x80x2-bis(4-aminophenoxy)-diphenylsulfide, bis[2-(4-aminophenyl)-benzothiazolyl]ether, bis[2-(4-aminophenyl)-benzimidazolyl]sulfoxide, bis[2-(4-aminophenyl)-benzoxazolyl], 4-(4-aminophenylsulfonyl)-4xe2x80x2-aminobiphenyl, 4,4xe2x80x2-bis(4-aminophenyl)diphenylether and 1,4-di-(4-aminobenzoyloxy)butane. Of the aromatic diamino compounds under conditions (iii-1)xe2x80x2 to (iii-4)xe2x80x2, the aromatic diamino compounds under conditions (iii-2)xe2x80x2 and (iii-3)xe2x80x2 are preferred because polyimides obtained by heat-curing the photosensitive composition achieve high heat resistance, tensile strength and water resistance when they are used. Since the heat resistance, tensile strength and water resistance of the polyimides are further improved, of the aromatic diamino compounds under condition (iii-2)xe2x80x2, bis[4-(3-aminophenoxy)phenyl]sulfone, 3,3-diaminodiphenylsulfone, 1,3-bis(3-aminophenoxy)benzene and 4,4xe2x80x2-bis(3-aminophenoxy)biphenyl are more preferred; and, of the aromatic diamino compounds under condition (iii-3)xe2x80x2, bis[4-(4-aminophenoxy)pnenyl]sulfone, 4,4xe2x80x2-diaminobenzophenone, 4,4xe2x80x2-bis[4-(4-aminophenoxy)phenoxy]-diphenylsulfone, 4,4xe2x80x2-diaminodiphenylsulfoxide and 4,4xe2x80x2-aiaminodiphenylsulfone are more preferred.
Representative examples of component (B) used as a photopolymerization initiator include benzophenone derivatives such as benzophenone, o-benzoyl methyl benzoate, 4-benzoyl-4xe2x80x2-methyl diphenyl ketone, dibenzyl ketone and fluorenone; acetophenone derivatives such as 2,2xe2x80x2-diethoxyacetophenone, 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-2-methyl propiophenone; thioxanthaone derivatives such as thioxanthone, 2-methylthioxanthone, 2-isopropyl thioxanthone and diethyl thioxanthone; benzyl derivatives such as benzyl, benzyl dimethyl ketal and benzyl-xcex2-methoxyethyl acetal; benzoin derivatives such as benzoin and benzoin methylether; azido derivatives such as 2,6-di(4-azidobenzylidene)-4-methylcyclohexanone and 2,6-di(4-azidobenzylidene)cyclohexanone; and oxime derivatives such as 1-phenyl-1,2-butadione-2-(O-methoxycarbonyl)oxime, 1-phenyl-1,2-propanedione-2-(O-methoxycarbonyl)oxime, 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime, 1-phenyl-1,2-propanedione-2-(O-benzoyl)oxime, 1,3-diphenylpropanetrione-2-(O-ethoxycarbonyl)oxime and 1-phenyl-3-ethoxy-propanetrione-2-(O-benzoyl)oxime. Of these, oxime derivatives are preferred for its high photosensitivity. The amount of the photopolymerization initiator is preferably in the range of from 1 to 15 parts by weight per 100 parts by weight of polyimide precursor.
Representative examples of component (C) used as solvents include N,Nxe2x80x2-dimethylformamide, N-methylpyrrolidone, N-acetyl-2-pyrrolidone, N,Nxe2x80x2-dimethylacetamide, diethylene glycol dimethylether, cyclopentanone, xcex3-butyrolactone and xcex1-acetyl-xcex3-butyrolactone. They may be used individually or in combination. These solvents may be employed in the range of from 100 to 400 parts by weight per 100 parts by weight of the polyimide precursor according to thickness of the films or viscosity of the composition.
The compounds having a reactive carbon-carbon double bond can be used in addition to the above-mentioned components (A) to (C) to improve photosensitivity of the present composition, if desired. Representative examples of such compounds include 1,6-hexandioldiacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate having 2 to 20 of repeating units, pentaerythritol diacrylate, dipentaerythritol hexacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, methylene bisacrylamide, N-methylolacrylamide, and corresponding methacrylate and methacrylamide to the above-mentioned compounds. These compounds may be employed in the range of from 1 to 30 parts by weight per 100 parts by weight of the polyimide precursor.
Sensitizers can be used to improve photosensitivity of the present composition, if desired. Representative examples of the sensitizers include Michler""s ketone, 4,4xe2x80x2-bis(diethylamino)benzophenone, 2,5-bis(4-diethylaminobenzylidene)cyclopentanone, 2,6-bis(4-diethylaminobenzylidene)cyclohexanone, 2,6-bis(4-dimethylaminobenzylidene)-4-methylcyclohexanone, 2,6-bis(4-diethylaminobenzylidene)-4-methylcyclohexanone, 4,4xe2x80x2-bis(dimethylamino)chalcone, 4,4xe2x80x2-bis(diethylamino)-chalcone, 2-(4xe2x80x2-dimethylamino cinnamylidene)indanone, 2-(4xe2x80x2-dimethylamino benzylidene)indanone, 2-(p-4xe2x80x2-dimethyl-aminobiphenyl)-benzothiazole, 1,3-bis(4-dimethylaminobenzylidene)acetone, 1,3-bis(4-diethylaminobenzylidene)-acitone, 3,3xe2x80x2-carbonyl-bis(7-diethylamino coumarin), 3-acetyl-7-dimethylamino coumarin, 3-ethoxycarbonyl-7-dimethylamino coumarin, 3-benzyloxycarbonyl-7-dimethylamino coumarin, 3-methoxycarbonyl-7-diethylamino coumarin, 3-ethoxycarbonyl-7-diethylamino coumarin, N-ethyl-N-phenyl-ethanolamine, N-phenyldiethanolamine, N-p-tolyldiethanolamine, N-phenyl-ethanolamine, 4-morpholino-benzophenone, 4-dimethylamino isoamylbenzoate, 4-diethylamino isoamylbenzoate, 2-mercaptobenzimidazole, 1-phenyl-5-mercapto-1,2,3,4-tetrazole, 2-mercapto-benzothiazole, 2-(p-dimethylaminostyryl)-benzoxazole, 2-(p-dimethylaminostyryl)-benzthiazole, 2-(p-dimethylaminostyryl)naphtho(1,2-d)-thiazole and 2-(p-dimethylaminobenzoyl)styrene. Of these, a combination of compounds having a mercaptho group and compounds having a dialkylaminophenyl group is preferred for its sensitivity. They may be used individually or in combination of two to five compounds. The amount of the sensitizer is preferably in the range of from 0.1 to 10 parts by weight per 100 parts by weight of the polyimide precursor.
An adhesion promoter can be added to the composition of the present invention to improve an adhesive strength, if desired. Representative examples of the promoter include xcex3-aminopropyltrimethoxysilane, N-(xcex2-aminoethyl)-xcex3-aminopropylmethyldimethoxysilane, xcex3-glycidoxypropylmethyldimethoxysilane, xcex3-glycidoxypropylmethyldiethoxysilane, xcex3-mercapthopropylmethyldimethoxysilane, 3-methacryloxypropyldimethoxymethylsilane, 3-methacryloxypropyltrimethoxysilane, dimethoxymethyl-3-piperidinopropylsilane, diethyoxy-3-glycidoxypropylmethylsilane, N-(3-diethoxymethylsilylpropyl)succinimide, N-[3-(triethoxysilyl)propyl]phthalamic acid, benzophenone-3,3xe2x80x2-bis(3-triethoxysilylpropylaminocarbonyl)-4,4xe2x80x2-dicarboxylic acid and benzene-1,4-bis(3-triethoxysilylpropylaminocarbonyl)-2,5-dicarboxylic acid. The amount of the promoter is preferably in the range of from 0.5 to 10 parts by weight per 100 parts by weight of the polyimide precursor.
A polymerization inhibitor can be added to the composition of the present invention to improve stability of sensitivity and viscosity of the composition solution in preservation, if desired. Representative examples of the inhibitor include hydroquinone, N-nitrosodiphenylamine, p-tert-butylcatechol, phenothiazine, N-phenylnaphthylamine, ethylenediamine tetraacetic acid, 1,2-cyclohexanediamine tetraacetic acid, 2xe2x80x2,2xe2x80x2-diethyletherdiamine tetraacetic acid, 2,6-di-tert-butyl-p-methylphenol, 5-nitroso-8-hydroxyquinoline, 1-nitroso-2-naphthol, 2-nitroso-1-naphtol, 2-nitroso-5-(N-ethyl-N-sulfopropylamino)phenol, N-nitroso-N-phenylhydroxylamine ammonium salt, N-nitroso-N-(1-naphthyl)-hydroxylamine ammonium salt and bis(4-hydroxy-3,5-tert-butylphenyl)methane. The amount of the inhibitor is preferably in the range of from 0.005 to 5 parts by-weight per 100 parts by weight of the polyimide precursor.
In the present invention, it is necessary that the absorbance at 365 nm wavelength (i-line) light of a 10 xcexcm thick dried coating obtained from a polyimide precursor composition be 1.5 or less to form a pattern on the film with i-line wavelength light. When the absorbance is over 1.5, the light intensity is not sufficient at the bottom of the film so that a satisfactory pattern is not formed.
The above-mentioned absorbance can be adjusted by the amounts of essential components (A) to (C) and other additives.
The photosensitive compositions of the present invention can be produced by mixing the above-mentioned components (A) to (C) and others And, from the thus obtained composition, a polyimide film can be obtained by taking steps as descirbed below.
The compositions of the present invention are applied on a substrate by using, for instance, a spin-coater, a bar-coater, a blade-coater, a curtain-coater, screen printing press and a spray-coater.
The resultant coating can be dried by air-drying, heating in an oven or on a hot plate, and vacuum drying.
The dried coating should be exposed with a ultraviolet ray, etc. as a light source by using an exposure equipment such as a contact aligner, a mirror projection aligner and a stepper. Of these, a stepper and i-line as a light source are preferred for its high resolution and easy handling.
The irradiated film can be developed by conventional methods for developing photoresist such as a spin-spray method, a puddle method and a dipping method with a supersonic wave. Preferably, a developing solution is a combination of good and poor solvents to the above-mentioned polyimide precursor. Representative examples of good solvents include N-methylpyrrolidone, N-acethyl-2-pyrrolidone, N,Nxe2x80x2-dimethylacetamide, cyclopentanone, cyclohexanone, xcex3-butyrolactone, xcex1-acethyl-xcex3-butyrolactone. Representative examples of poor solvents include toluene, xylene, methyl alcohol, ethyl alcohol, isopropyl alcohol and water. The ratio of both solvents is adjusted according to the solubility of the polyimide precursor. They may be used in combination. If necessary, when the polyimide precursor contains carboxylic acids, the aqueous solution of organic bases such as cholinehydroxide and tetra-methylammonium hydroxide can be used as a developing solution, or used by being added to the above-mentioned organic solvents according to the solubility of the polyimide precursor.
The resultant patterned film are heat-cured to obtain a polyimide film as a result of evaporation of volatile components. This process can be carried out by using a hot plate, an oven, and an oven capable of storing temperature program. Air, nitrogen and inert gas such as argon may be used as an atmosphere in heat-curing the patterned film.
The present invention is now described in more detail by referring to Examples, but the scope thereof is not restricted by them.
Each characteristic of the compositions in Examples and Comparative Examples was determined as follows:
(1) Amide Bond Density
Amide bond density [C] is calculated according to the equation below.       [    C    ]    =      2000                            [          M          ]                C            +                        [          M          ]                A            +                        [          M          ]                S            
In the equation, [M]C represents the molecular weight of a tetracarboxylic acid unit, and it is calculated by subtracting 32 (=the atomic weight of oxygen atomxc3x972) from the molecular weight of an ATC dianhydride used as a starting material. When two or more of ATC dianhydrides are employed, their average molecular weight is used for the calculation. [M]A represents the molecular weight of an aromatic diamine unit, and it is calculated by subtracting 2 (=the atomic weight of hydrogen atomxc3x972) from the molecular weight of an aromatic diamino compound used as a starting material. When two or more of the aromatic diamino compounds are employed, their average molecular weight is used for the calculation. [M]S represents the total amount of substituting groups R and Rxe2x80x2 which bind to aromatic rings through carbonyl group in the polyimide precursor, and it is calculated by doubling the average molecular weight of R and Rxe2x80x2 radicals. The atomic weights used in the above calculation are 12 for carbon, 14 for nitrogen, 16 for oxygen, 32 for solfur and 1 for hydrogen, respectively. A numerator 2000 is the coefficient to calculate the mole value of amide bonds per 1 kg of the polyimide precursor.
(2) Absorbance of Polyimide Precursor
N-methylpyrrolidone solution of polyimide precursor is applied on a 1 mm thick quartz plate using a spin-coater and dried in an oven at 80xc2x0 C. for 40 min. to form a 10 xcexcm thick polyimide precursor coating. Then, its absorbance (referred to hereinafter as precursor absorbance) at 365 nm is measured by ultraviolet spectroscope UV-240 type (manufactured by Shimazu Corporation) and is calculated according to the following equation:
Absorbance=log10 I0/I
(wherein I0 represents incident light intensity; I represents transmitted light intensity through a film.)
(3) Absorbance of Photosensitive Composition Coating
A photosensitive composition is applied on a 1 mm thick quartz plate using a spin-coater and dried in an oven at 80xc2x0 C. for 40 min. to form a 10 xcexcm thick photosensitive composition coating. Then, its absorbance (referred to hereinafter as coating absorbance) is measured by the same method as (2).
(4) Viscosity Number of Polyimide Precursor
Viscosity number (xcex7sp/c) of polyimide precursor in N-methylpyrrolidone (1 g/dl) is measured by Auto Viscometer AVL-2C (manufactured by San Denshi Ind. Co., Ltd.) at 30xc2x0 C.
(5) Viscosity of Photosensitive Composition
Viscosity of the photosensitive composition solution is measured by an E type viscometer (manufactured by Tokyo Keiki Co., Ltd.: VISCONIC-EMD type) at 23xc2x0 C.
(6) Tensile Strength and Elongation of Polyimide Film
In each Example, the general procedure is repeated except that the obtained film on the wafer is exposed without a photomask and is not developed. The resultant polyimide film is peeled from the wafer, and its tensile strength and elongation are measured according to ASTM D-882-88.
(7) Pull Test
Adhesive strength between a polyimide film and a silicon wafer is measured as follows. After the photosensitive composition on the wafer is heat-cured, a pin having a diameter of 2 mm is attached to the polyimide film with epoxy resin adhesive (Araldite(copyright) standard manufactured by Showa Highpolymer Co., Ltd.). The obtained sample is subjected to a pull test using a pull tester (manufactured by Quad Company Group, SEBASTIAN 5 type).
The standard of judgement:
(8) Water Resistance Test
After the photosensitive composition on the wafer is heat-cured, it is kept in boiling water for 48 hrs. and dried in an oven at 50xc2x0 C. for 2 hrs. Then, it is subjected to the above-mentioned pull test.
The standard of judgement:
(9) Raw Material
ATC dianhydrides used in Preparations are represented by the following symbols. The structural formulas shown below represent X in the general formula (VI).
X-1: 3,3xe2x80x2,4,4xe2x80x2-benzophenone tetracarboxylic dianhydride 
X-2: 3,3xe2x80x2,4,4xe2x80x2-diphenylether tetracarboxylic dianhydride 
X-3: 3,3xe2x80x2,4,4xe2x80x2-diphenylsulfone tetracarboxylic dianhydride 
X-4: 3,3xe2x80x3,4,4xe2x80x3-terphenyltetracarboxylic dianhydride 
X-5: 1,4-bis(3,4-dicarboxylbenzoyl)benzene dianhydride 
X-6: 4,4xe2x80x2-bis(3,4-dicarboxylphenoxy)bipheny dianhydride 
X-7: 4,4xe2x80x2-bis(3,4-dicarboxylphenoxy)diphenyl sulfone dianhydride 
X-8: 3,3xe2x80x2,4,4xe2x80x2-biphenyl tetracarboxylic dianydride 
X-9: 1,4-dimetoxy-2,3,5,6-benzene tetracarboxylic dianhydride 
X-10: 3,3xe2x80x2,4,4xe2x80x2-diphenylmethane tetracarboxylic dianhydride 
X-11: pyromellitic dianhydride 
Aromatic diamino compounds used in the Preparations are represented by the following symbols. The structural formulas shown below represent Y in the general formula (VII).
Y-1: 4,4xe2x80x2-bis(4-aminophenoxy)biphenyl 
Y-2: 9,10-bis(4-aminophenyl)anthracene 
Y-3: bis [4-(4-aminophenoxy)phenyl]ether 
Y-4: bis[4-(3-aminophenoxy)phenyl]sulfone 
Y-5: 3,3xe2x80x2-diaminodiphenylsulfone 
Y-6: 1,4-bis(4-aminophenoxy)benzene 
Y-7: 1,3-bis(3-aminophenoxy)benzene 
Y-8: bis[4-(4-aminophenoxy)phenyl]sulfone 
Y-9: 4,4xe2x80x2-bis(3-aminophenoxy)biphenyl 
Y-10: 4,4xe2x80x2-diaminodiphenylether 
Y-11: p-phenylene diamine 
Y-12: 4,4xe2x80x2-diaminodiphenylsufide 
Y-13: 4,4xe2x80x2-diaminobenzophenone 
Y-14: 4,4xe2x80x2-bis[4-(4-aminophenoxy)phenoxy]diphenylsulfone 
Y-15: 3,4xe2x80x2-diaminodiphenylether 
Y-16: 4,4xe2x80x2-diaminodiphenylsulfoxide 
Y-17: 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminobiphenyl 
Y-18: 2,4-diaminomesitylene 
Y-19: m-phenylene diamine 
Y-20: 4,4xe2x80x2-diaminodiphenylsulfone 
Y-21: 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane 
Y-22: 3,5-diamino ethylbenzoate 
Y-23: 2,4-diaminobenzamide 
Y-24: 3,5-diaminobenzophenone 
Y-25: 3,5-diamino(2-methacryloxyethyl)benzoate 
Y-26: 3,5-diaminobenzonitrile 
Y-27: 2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane 
Y-28: 4,4xe2x80x2-diamino-3,3xe2x80x2,5,5xe2x80x2-tetramethyldiphenylmethane 
Compounds used in the Preparations to form xe2x80x94COR or xe2x80x94CORxe2x80x2 groups (R-raw material) are represented by the following symbols.
E-1: 2-hydroxyethyl methacrylate 
E-2: 2-isocyanateethyl methacrylate 
E-3: 2-diethylamino ethyl methacrylate 
E-4: glycidyl methacrylate 
E-5: 2-hydroxyethyl acrylate 
E-6: N-(2-hydroxyethyl)methacrylamide 
E-7: (2-hydroxypropyl)acrylamide 
E-8: 2-metacryloxyethyltrimethylammoniumhydroxide 
E-9: ethyl alchol
C2H5OH